A 69-year-old male presents with bilateral lower extremity edema for 4 months. Lab results from 4 months ago show: Hb 150g/L, urinalysis (UA) protein-positive, 24-hour urinary protein quantification 5.9g, plasma albumin (Alb) 19.2g/L, serum creatinine 108μmol/L. The diagnosis is: